The present invention relates to a laminated heat exchanger which may be employed as an evaporator, an oil cooler or the like in an air conditioning system for vehicles, and more specifically, it relates to a laminated heat exchanger that employs tube elements each having tanks and a heat exchanging medium passage formed as an integrated unit.
A laminated heat exchanger proposed by the applicant of the present invention, which is constituted by laminating over a plurality of levels tube elements each having a pair of tanks and a heat exchanging medium passage communicating between the tanks formed as an integrated unit is disclosed in Japanese Unexamined Patent Publication No. H 4-356690.
To explain the structure of the main tube elements that may constitute this heat exchanger in reference to FIG. 13, a tube element 100 is provided with a pair of tanks 101 and 101 and a U-shaped heat exchanging medium passage 102 communicating between the tanks 101, with communicating holes 103 for communicating with adjacent tanks 101 formed at the two sides of the tanks 101. In each of formed plates 104 that constitute the tube elements 100, as shown in FIG. 14, two bowl-like distended portions for tank formation 105 and 105 are formed at one end in its lengthwise direction and a distended portion for passage formation 106 is formed continuous thereto, although the distended portion for passage formation 106 is only partially shown in the figure. A projection 107 extends out from the area between the two distended portions for tank formation 105 and 105 toward the distended portion for passage formation 106. Although not shown in the figure, the projection 107 extends to the vicinity of the other end of the formed plate 104. In addition, an indented portion 108 for mounting a communicating pipe (not shown) is provided between the two distended portions for tank formation 105 and 105. In the distended portion for passage formation 106, a plurality of shoal-like beads 109 are formed as extended protuberances near the distended portions for tank formation 105 and 105.
Thus, when such tube elements 100 are laminated over a plurality of levels with corrugated fins 111 provided in between them, the direction in which the heat exchanging medium passage 102 communicating between a pair of tanks 101 and 101 in each tube element 100 and the direction that the heat exchanging medium takes when flowing through the tanks 101 and the communicating holes 103 of adjacent tube elements 100, i.e., the direction of the lamination of the tube elements 100, are perpendicular to each other.
However, in the heat exchanger disclosed in the publication mentioned above, the heat exchanging medium passage 102 maintains an almost consistent flow area from the side opposite from the tanks through the side where the tanks 101 are provided. In other words, since the heat exchanging medium passage 102 is formed linearly, wall surfaces 110 at the two sides of the shoal-like beads 109 located near the tanks 101 in the heat exchanging medium passage 102 are continuous to and in contact with the walls at the tanks 101 toward heat exchanging medium side approximately at a right angle. In addition, the flow area of the heat exchanging medium passage 102 at the point where it communicates with the tank 101 is normally smaller than the opening area of the communicating holes 103 that communicate between the tanks in tank groups, since, at that point, the heat exchanging medium flows past the two sides of the shoal-like beads.
Because of this, when a portion of the heat exchanging medium flowing through the tanks 101 in the direction of the lamination via the communicating holes 103 flows into the heat exchanging medium passages 102, the heat exchanging medium must make a right-angle turn, as indicated by the arrow in FIG. 13. Moreover, since the flow area of the heat exchanging medium passage 102 at the boundary between the heat exchanging medium passage and the tanks 101 is considerably smaller than the opening area of the communicating holes 103 at the tanks 101, the heat exchanging medium encounters a large resistance when it flows into the heat exchanging medium passages 102 from the tanks 101. Consequently, at locations where the heat exchanging medium flows at high speed, in particular, heat exchanging medium does not readily flow into the heat exchanging medium passages 102 from the tanks 101 due to the increased resistance, resulting in inconsistency in the distribution of the heat exchange which, in turn, leads to a concern that the heat exchanger does not perform to its full capacity.